What Is An Interference Engine?

Are you thinking about getting an interference engine, or are you curious about interference engines? Either way, you came to the right place. Alaina took some time to provide a good explanation of what an interference engine is. She also explains the biggest issue to look for in interference engines:

Now, let’s answer some commonly asked questions:

What Is An Interference Engine?

An interference engine is designed so the valves and pistons occupy the same space in the combustion chamber, but at slightly different moments in time. If the timing of the valves is disrupted, the pistons and valves will interfere with each other. Interference engines are very common among modern four-stroke engine applications. The design allows for higher compression ratios than non-interference engines can typically achieve. Higher compression ratios allow the engine to create more power.

Can You Modify An Interference Engine To Get More Power Out Of It?

Yes, you can modify an interference engine in all the same ways that you might modify a non-interference engine.

What Common Problems Does An Interference Engine Have?

Interference engines have one big drawback. The valves and pistons can collide. A valve and piston collision is a big problem that causes severe engine damage. When the valves are in the fully open position, they’re able to extend into the same areas where the pistons are. Interference engines depend on the crankshaft and the timing belt or chain to keep the pistons away from the valves. When the timing belt or chain fails, the timing is thrown off. This causes the valves to collide with the pistons.

In the video, Alaina describes the scenario well:

“When your timing chain or belt breaks on the road, the camshaft stops turning. By way of inertia, the crankshaft is going to keep turning. This means you have open valves and pistons that are able to extend into those valves. The valves and pistons are going to collide. The valve is going to bend or break.”

If this happens to your interference engine, you’ll have to either rebuild or replace your engine.

How To Check For Damage In An Interference Engine

The best way to confirm that a valve and piston collision occurred in an interference engine is to have a mechanic perform a leak down test. A leak down test checks to see where compression is “leaking” from the combustion chamber. Also, on some engines, the upper end of the valve stem can be inspected by pulling the valve cover.

How To Prevent Valve And Piston Collisions In An Interference Engine

The good news is valve and piston collisions aren’t inevitable. You can prevent this situation by replacing your timing belt on schedule. A broken timing belt is the most common cause of damage in an interference engine. Some interference engines have timing chains instead of timing belts. These rarely break, so there’s not much to worry about.